Treatment of waste liquor from pulp production

ABSTRACT

A process and apparatus for treating concentrated spent liquor from a soda-based pulping process to recover sodium for reuse in the pulping process and to prevent the usual pollution of streams and air caused by the usual effluent from the pulping process. The process and apparatus comprises the following steps and apparatus. Concentrated spent liquor containing sodium is mixed with recycled finely-divided reactive alumina hydrate and formed into solid pellets by spraying the concentrated liquor-aluminum hydrate mixture onto a bed of recycled sodium aluminate furnace ash in an enclosed rotating container and tumbling the mixture and ash. The solid pellets are combusted and reacted by feeding the pellets through a furnace operating at a temperature below the fusion temperature of sodium aluminate and at a sufficiently high temperature to combust the organic portion of the pellets and react the sodium content thereof with the alumina to form additional sodium aluminate as a particulate unfused ash. The resulting furnace ash is pulverized and a portion thereof is recycled for subsequent reuse in the treating process. The remaining portion of the ash is dissolved in water to form a solution of sodium aluminate. The sodium aluminate solution is reacted with either sulphur dioxide or carbon dioxide or both to form sodium sulfite and/or sodium carbonate pulping chemical and alumina and alumina is separated for reuse in the treating process.

llnited States Patent 1191 Sheeley et a1.

[ Jan. 22, 1974 TREATMENT OF WASTE LIQUOR FROM PULP PRODUCTION [75]Inventors: Donald R. Sheeley; James H. Rion;

William R. Cook; William A. Biggs, Jr., all of Hartsville, SC.

[73] Assignees Sonoco Products Company,

l-lartsville, SC.

[22] Filed: Mar. 28, 1972 [21] Appl. No.: 238,776

Related US. Application Data [63] Continuation-in-part of Ser. No.37,184, May 14,

1970, abandoned.

[52] US. Cl 162/36, 162/30, 162/240, 423/207 [51] Int. Cl D2lc 11/02,D2lc 11/12 [58] Field of Search 162/30, 36, 239, 240; 423/207, 423/121;26l/DlG. 54

[56] References Cited UNITED STATES PATENTS 3,061,408 10/1962 Liirie162/36 x 2,734,796 2/1956 Ashley at 111.. 423/121 3,488,039 1/1970 Ekman26l/DIG. 54

' Primary ExaminerArthur D. Kellogg Assistant ExaminerAlfred DAndrea,Jr. Attorney, Agent, or FirmWarley L. Parrott et a].

WMHEEH' [57] ABSTRACT A process and apparatus for treating concentratedspent liquor from a soda-based pulping process to recover sodium forreuse in the pulping process and to prevent the usual pollution ofstreams and air caused by the usual effluent from the pulping process.The process and apparatus comprises the following steps and apparatus.Concentrated spent liquor containing sodium is mixed with recycledfinely-divided reactive alumina hydrate and formed into solid pellets byspraying the concentrated liquor-aluminum hydrate mixture onto a bed ofrecycled sodium aluminate furnace ash in an enclosed rotating containerand tumbling the mixture and ash. The solid pellets are combusted andreacted by feeding the pellets through a furnace operating at atemperature below the fusion temperature of sodium aluminate and at asufficiently high temperature to combust the organic portion of thepellets and react the sodium content thereof with the alumina to formadditional sodium aluminate as a particulate unfused ash. The resultingfurnace ash is pulverized and a portion thereof is recycled forsubsequent reuse in the treating process. The remaining portion of theash is dissolved in water to form a solution of sodium aluminate. Thesodium aluminate solution is reacted with either sulphur dioxide orcarbon dioxide or both to form sodium sulfite and/or sodium carbonatepulping chemical and alumina and alumina is separated for reuse in thetreating process.

9 Claims, 4 Drawing Figures NSOLVEE.

Pmnmmzzlsu 3" 8 THm 5mm! SuPPLY TREATMENT OF WASTE LIQUOR FROM PULPPRODUCTION This application is a continuation-in-part of Ser. No.37,184, filed May 14, 1970, now abandoned.

This invention relates to a process and apparatus for treatment of wasteliquor from pulping processes and more particularly to treatingconcentrated spent liquor from a soda-based pulping process to recoversodium for reuse in the pulping process and to prevent the usualpollution of streams and air caused by the usual effluent from thepulping process. Additionally, the process and apparatus may be utilizedfor treating concentrated spent liquor from soda-based sulfite pulpingprocesses to recover sulfur and sodium for reuse in the pulping process.

In prior practices of sodium and sulfur recovery from spent liquor, thedilute spent liquor generally is concentrated by evaporation and thenburned in a Kraft-type furnace to produce a smelt composed of a mixtureof principally sodium carbonate and sodium sulfide. The smelt issubsequently processed by several means to recover the sodium as sodiumsulfite either with or without the recovery -of sulfur. Examples ofprocesses which recover sodium and sulfur as sodium sulfite fromKraft-type furnace smelts are set forth in US. Pat. Nos. 2,792,350;2,862,887; 2,864,669; 2,849,292 and 3,061,408.

In one embodiment of the process disclosed in the above U. S. Pat. No.3,061,408, either silica, alumina and silica (Feldspar) or alumina aloneas reactants are mixed with the concentrated spent liquor beforecombusting. In the combusting step, the reactant chosen reacts with thesodium content of the liquor to form either sodium silicate, a mixtureof sodium silicate and sodium aluminate, or sodium aluminate,respectively. The sulfur content of the liquor is released into flue gasfrom the furnace as sulphur dioxide. In the event that the desiredreaction does not go to adequate completion during the residence time inthe furnace, an auxiliary furnace of the glass-making type is providedto subsequently complete the reactions. The process may work fairly wellwhere silica or silica and alumina (Feldspar) are the reactants since atthe normal Krafttype furnace temperatures of 1800 to 2000 F., thereaction products would be in the molten, fluid state and could becontinuously removed from the furnace base by gravity out-flow forsubsequent processing as in normal Kraft-type furnace operations.

In the case of alumina, essentially alone as the reactant, the processwill not operate satisfactorily as specified in either a glass furnaceor a Kraft furnace. This is due to the fact that both the alumina andthe sodium aluminate reaction product in this case are solid, re-

' fractory finely-divided particulate materials at the usual Kraft andglass furnace temperatures since both have melting points of 3000" F. ormore. This being the case with a Kraft furnace, which has a solidbottom, there is no way to continuously remove the particulate productfrom the furnace by conventional means. Indeed, the product will notaccumulate in the furnace bottom as it does with smelt. The reason forthis is best understood by reviewing the operation of a Kraft furnace.

In the normal operation of a Kraft-type furnace with concentrated spentliquor, the liquor is sprayed into the secondary air burning zone nearthe middle of the vertica] furnace section where excess combustion ofdraft air is supplied. The water content is evaporated from the atomizedliquor and the liquor solids are charred or partially burned attemperatures of about 1800 F. The charred ash falls to near the furnacebottom to form an ash bed which floats on the molten smelt product.Primary draft air, deficient in oxygen, is continuously blown throughthe ash bed to reduce sodium compounds to sodium sulfide and sodiumcarbonate as smelt, which continuously flows out the furnace bottom forsubsequent processing. When Kraft spent liquor is processed in thefurnace, sodium sulfate as make-up chemical at the rate of about 50 to150 pounds per ton of pulp produced is mixed in particulate form withthe concentrated liquor just before being sprayed into the furnace. Thismake-up chemical is needed to off-set sodium and sulfur losses which arelost mainly in the flue gas in extremely fine form during the combustionand are partially recoverable at electrostatic precipitators which aredesigned to treat the flue gas for its recovery.

In the case of combusting spent liquor containing particulate aluminareactant for carrying out the process of the above US. Pat. No. 3,061,408, a similar loss of reactant will occur. in addition and much moreserious, the primary draft air through the ash bed and the secondarydraft air above it will carry what finelydivided particulate sodiumaluminate is formed out of the furnace in the flue gas. Thus, as statedabove, the process of prior Pat. No. 3,061,408, using alumina as thereactant, is not practical and will not work as specified in a Kraft orglass furnace due to reactant and product loss unless temperatures wellover 3000 F. are maintained which is uneconomical in both fuel demandnisftastgry.1J1ai n9q$t- Accordingly, it is the object of the presentinvention to overcome the above problems and to provide a practicalcommercial process and apparatus which may be used in mill operations. 7g i In accordance with this invention, it has been discovered that wasteliquor treating processes which normally require the use of expensiveKraft-type or glass furnaces and which convert the sodium and sulfurcontent to a molten smelt, can be simplified and the process carried outsatisfactorily with relatively inexpensive furnace equipment such as arotary kiln. This discovery is based on reacting the sodium content ofthe waste liquor, having a solids content of about 25 per cent topercent, with alumina or its hydrate in a combustion process to formsodium aluminate and providing a sufficient amount of sodium aluminateto maintain the waste liquor, including organic solids and water, in asolid pellet, non-sticky form. This form is maintained during the dryingand combustion process at temperatures below the fusion point of thealuminate (about 3000 F.). The sodium aluminate avoids the usualconversion of the waste liquor inorganic solids into a molten stickysmelt and avoids the necessity of sisnqn iy siy msm, ea izes!.fsztl ad isiam More specifically, it has been found that the above 7 object may beaccomplished by providing a process and apparatus for treatingconcentrated spent liquor from soda-based pulping processes to recoversodium for reuse in the pulping process and to prevent the usualpollution of streams and air caused by the usual effluent from thepulping process. Basically, the process and apparatus of this inventioncomprises mixing concentrated spent liquor containing sodium from asodabased pulping process with recycled finely divided reactive sluminahydrate in an amount necessary to react with the soda content of theliquor for ultimate formation of sodium aluminate as the reactionproduct. Solid pellets are formed from the concentrated liquoraluminumhydrate mixture in a rotating enclosed tumbling apparatus carrying a bedof recycled sodium aluminate furnace ash in the bottom thereof byspraying the concentrated liquor-aluminum hydrate mixture onto the bedof ash so that as the tumbling means rotates, solid pellets will beformed. The thus formed solid pellets are combusted and reacted byfeeding the pellets through a furnace operating at a temperature belowthe fusion temperature of sodium aluminate and at a sufficiently hightemperature to combust the organic portion of the pellets and react thesodium content thereof with the alumina to form additional sodiumaluminate as a particulate unfused ash. The furnace ash is pulverizedand a portion thereof is recycled for subsequent reuse in the treatmentprocess. The remaining portion of the ash is dissolved in water to forma solution of sodium aluminate. The sodium aluminate solution in oneinstance is reacted with sulphur dioxide to form sodium sulfite andalumina hydrate and the alumina hydrate is separated for reuse in thetreating process and the sodium sulfite for reuse in the pulpingoperation.

In obtaining the commercially important features of our process asdescribed above, and particularly the sodium aluminate absorptivecarrier material, we employ a molar ratio of N320 to A1 of about 1 :lto.2: 1. This ratio might be increased in some instances if desired toabout 3:1. In any ratio used, however, it is' important to have thealumina present to react with the sodium to the extent that the usualformation of sodium sulfide and sodium carbonate and the formation of asticky molten smelt is avoided. V V

Some of the objects and advantages of this invention having been stated,other objects and advantages will appear as the description proceeds,when taken in conjunction with the accompanying drawings in which FIG. 1is a schematic, diagrammatic flow diagram of the process and apparatusof this invention;

FIG. 2 is a schematic, diagrammatic view of the pellet forming apparatusutilized in this invention;

FIG. 3 is a schematic, diagrammatic view of the absorber apparatusutilized in this invention; and

FIG. 4 is an enlarged partial view of a portion of the interior of theabsorber apparatus of FIG. 3.

Referring now to the drawings, the following is a general description ofthe process and apparatus of this invention.

Dilute waste liquor containing sodium from a sodabased pulping operationor pulp plant is concentrated in multiple effect evaporators, not shown,and sent to a heavy liquor storage tank 10. From the heavy liquorstorage tank 10, the concentrated liquor is pumped to a repulper 12through enclosed conduit 11. Alumina cake from the belt 13 of beltwasher 14 drops into the repulper l2 and is mixed with the liquor. Adescription of how the alumina cake is formed in the belt washer 14 willbe given below. The resulting slurry is pumped into a mixer tank 16through conduit 15. In the mixer tank 16, the liquor and alumina arethoroughly mixed and desired alumina make-up is added from the storagetank l7 by screw conveyor 18 so that a sufficient amount offinely-divided reactive alumina hydrate is mixed with the liquor toreact with the soda content thereof for the ultimate formation of sodiumaluminate as the reaction product.

From the mixing tank 16, the slurry is pumped through conduit 20 into apelletizer or pellet forming apparatus 21.

The pelletizer 21, as may be seen more particularly in FIG. 2, comprisesan enclosed hollow housing 22 which is mounted for rotation on anysuitable driving apparatus 23. The conduit 20 extends into andlongitudinally through the housing 22 and includes a plurality of spraynozzles 24 or other suitable devices for spraying the concentratedliquor-aluminum hydrate slurry within the housing 22. Connected innon-rotating arrangement with one end of the housing 22 is a screwconveyor 27 which feeds recycled sodium aluminate furnace ash from anelevator 30, screw conveyor 31 and ground ash bin 32 into the bottom ofthe enclosed housing 22 of the pelletizer 21 to form a bed of recycledsodium aluminate furnace ash in the bottom of the housing 22. As thehousing 22 rotates, the mixture of concentrate liquor-aluminum hydrateslurry sprayed therein will be tumbled with the furnace ash resulting inthe formation of more or less round, solid pellets.

The pellets so formed may range in size from about one-eighth inch toone inch or more in diameter. The quantity of dry sodium aluminatefurnace ash required to form these discrete pellets depends upon thewater content of the concentrated liquor used. At 50-60 percent solidsequal parts by weight are used. There is an apparentdehydration-hydration reaction between the liquor and the sodiumaluminate since considerable heat is involved in the pelletizing stepand the pellets are very cohesive and hard in spite of the watercontent.

In the pellet form, the liquor solids are incapsulated with the aluminareactant within the pellet.

The thus formed pellets are then fed by a chute 35 into one end of areaction furnace which may be any suitable type of inexpensive andsimple furnace, such as a rotary kiln, a multihearth furnace, or amoving grate furnace. In fact any type furnace can be utilized that isequipped to discharge a pelleted ash resulting from combustion from thebottom of the discharge end in the case of a rotary kiln. The furnacepreferably operates at a temperature below the fusion temperature ofsodium aluminate of about 3000 P. so that the reaction mass does notbecome plastic or sticky at any stage and preferably at a temperaturerange between 1500 F. 2000 F. to combust the organic portion of thepellets and react the sodium content thereof with the alumina to formadditional sodium alumina as a particulate unfused ash.

Thus, in the combustion process with sulfite spent liquor, a reducingatmosphere is inherently maintained for carrying out the basic reactionsregardless of the combustion conditions outside the pellets, as follows,for example:

Na SO, 2C Na s CO Na S O C0 Na s 50, C0

4 lignin S0 Na Na S Na,CO;, 3H S X CO X H O Na S AI203H2O N320 Has Na COA1 0 N320 Alg03 "l' CO2 In the oxidizing atmosphere outside of thepellets, the H 8 is oxidized and driven off as sulfur dioxide (S0 intothe gas stream:

The round pellets retain their form throughout the combustion stage andthe collection of the refractory sodium aluminate product as pelletsrather than fine ash is simplified and loss in the flue gas isminimized.

The rotary kiln 40 illustrated in FIG. 1 comprises an elongate enclosedchamber 41 which receives the uncombusted pellets at one end thereoffrom the chute 35 and allows the pellets to flow therethrough by gravityand by rotation of the chamber 41 toward the firing end of the furnace.The firing end of the furnace contains a burner 42 which produces aflame into the chamber 41.

The fully combusted and reacted pellets discharge from the firing end ofthe furnace 40 down a chute 45 and into an ash cooler 47. Secondarycombustion air is drawn from the atmosphere up through the cooler andcontacts the burned pellets thus cooling the pellets and preheating thecombustion air.

The cooled pellets (250 350 F.) pass down a chute 50 into a screwconveyor 51 and flow into an ash bin 53 by a bucket elevator 52. Fromthe ash bin 53, the pellets are fed into a granulator 55 where they areground to minus mesh and fed by way of a bucket elevator 56 into theground ash bin 32. As described above, a portion of the thus formedground sodium aluminate furnace ash is fed from the ground ash bin 32into the pelletizer 21 for reuse in the treatment process.

Returning to the gas flow through the process and apparatus of thisinvention, atmospheric air is drawn through the cooler 47 where it coolsthe pellets and preheats the air. This preheated air flows from thecooler 47 into the furnace 40 by conduit 60 where it joins hotcombustion gases from the burner 42 on the lower or firing end of thefurnace 40. These hot gases then meet the unreacted and uncombustedpellets flowing counter-currently through the furnace 40 and cause themto combust and react. The hot gases discharge from the input end of thefurnace 40 and into a cyclone 62 where laden dust is separated from thegas stream and returned by conduit 63 to the ground ash bin 32 or thescrew conveyor 31 leading therefrom.

The hot gases then flow through conduit 64 into a waste heat boiler 65where they are cooled to approximately 500 F. and at the same timegenerate steam for use elsewhere in the process and apparatus. Thesemicooled gases then flow through a conduit 67 into a direct contactgas cooler 68. In the gas cooler 68, the gases are contacted with waterwhich flows from a water supply 70, through conduit 71, through heatexchanger 72 and through conduit 73 into the cooler 68. The water isrecycled around and around in the gas cooler and exchanges its heat withfresh water in the heat exchanger 72. Gases are discharged from the gascooler at about 150 F. through conduit 76.

From the conduit 76, the gases pass through induced draft air fan 77,which originally causes atmospheric air to be drawn in through thecooler 47, and into an absorber 80. p

The absorber 80 comprises an elongate vertically extending hollowhousing 81 having a plurality of grids of spaced-apart, parallel,generally cylindrical bars ex-- tending transversely across the housing81. Alternate grids of bars 82 extend in opposite directions or atangles to each other so as to form venturi-like passages between thebars 82 and a generally checkerboard arrangement of grids of bars 82.These grids of bars 82 are disposed in generally the upper verticalportion of the enclosed housing 81 of the absorber 80.

Referring again to-the ground ash bin 32, the remaining portion of theground sodium aluminate furnace ash is fed by a screw conveyor 90 andconduit 91 into a dissolver or mixer tank 92 where it is slurried ormixed with water entering the dissolver 92 from conduit 93. This thinslurry consists of dissolved sodium aluminate plus any unreacted aluminaand other unsoluble materials that may be present in the ash. The thinslurry is pumped through conduit 95 to the top of the absorber 80 whereit is allowed to flow down over the grids of bars 82, as shown moreparticularly in FIG. 3 and 4, to meet the incoming cooled gases cominginto the bottom of the absorber. The sodium aluminate reacts with andabsorbs sulphur dioxide from the gas stream to form sodium sulfite andalumina in a thick slurry. The thick slurry is pumped from the base ofthe absorber 80 through conduit into an aging tank 101 and the cleanedair with sulphur dioxide removed is vented to the atmosphere throughvents 102 of the absorber 80.

The thick slurry is held in the aging tank 101 for approximately-20-60minutes allowing the alumina to age and coalesce so'that the slurry willbe easier to filter. The slurry flows from the aging tank throughconduit 103 into the belt washer filter apparatus 14. The belt 13rotating through the belt washer 14 filters out the alumina hydrate as adense cake and drops it into the repulper 12 for subsequent reuse in thetreatment process. The sodium sulfite solution passes through the belt13, through conduit 105 and into a vacuum receiver 106. From the vaccumreceiver 106, the sodium sulfite solution is pumped into sodium sulfitestorage tank through conduit 109 for subsequent use in the pulp mill andthe pulping processes.

The belt 13 of the belt washer 14 is continuously backwashed by waterfrom the belt wash tank 115. In the belt wash tank, water for use inback washing the belt 13 is trapped in a trough 116 and is pumpedthrough conduit 117 onto the belt 13. The contaminated water from thelower part of the belt wash tank is pumped to the mixer 92 through 93for use in making up the thin slurry in mixer 92. This results inrecovery of any alumina cake that is back washed from the belt 13. Waterfrom the belt 13 flows into the belt wash tank 115 through conduit 120.

Contaminated water from the gas cooler 68 overflows from the base of thecooler through conduit 122 and into a cake wash tank 123. Water from thecake wash tank 123 is pumped to the sprayers 125 by conduit 124 forspraying water on the belt 13 of the belt washer 14 to completely washthe sodium sulfite solution from the alumina cake. Any dust that iscollected in the contaminated water is recovered and added to the cakeand the dissolved sulphur dioxide is absorbed by the sodium sulfitesolution and is also recovered. Heated water from the heat exchanger 72is used for supplying hot make-up water through conduit to both the cakewash tank 123 and the belt wash tank 1 l5.

In accordance with the above general description of the process andapparatus of this invention, the following are illustrative,non-limiting, specific examples:

EXAMPLE 1 69,500 pounds per hour of 10% solids spent sulfite liquor isconcentrated in suitable multiple efiect evaporators to 13,540 poundsper hour of 51% concentrated liquor containing 1,330 pounds of sodium asNa O and 313 pounds of sulfur. The concentrated liquor is fed throughrepulper 12 and mixer 16 where it is intimately mixed with 4,860 poundsper hour of recycled freshing precipitated aluminum hydrate filter cakecontaining 2,920 pounds per hour of aluminum hydroxide, Al (01-1 Thismixture is fed to pelletizer 21 along with 16,460 pounds per hour ofrecycled sodium alumi nate kiln ash from the ground ash bin 32. In thepelletizer, the recycled ash forms more or less round solid pellets withthe concentrated liquor-aluminum hydrate mixture. The pellets arecontinuously fed from the pelletizer into the direct-fired rotary kiln40 where the pellets are combusted at a temperature of 1700 to 1800 F.The resulting combustion ash at the rate of 19,900 pounds per hour iscooled in the cooler 47 by the counter-current draft air; 16,460 poundsper hour of the ash is recycled continuously into the granulator 55,through the ash bin 32 and back into the pelletizer 21. 5,800 pounds perhour of the kiln ash is fed to the dissolver mixer 92 where 14,560pounds per hour of water are added to form a 20 percent solution ofsodium aluminate. This solution is fed to the absorber 80. Hot fluegases from the rotary kiln 41 containing water vapor, S CO etc., are fedthrough cyclone 62 where ash fines are precipitated and carried into theconveyor 31 from the ground ash bin 32. From the cyclone 20, the hotgases are carried through waste heat boiler 65 where heat is exchangedwith water to generate 15,000 pounds per hour of 150 pounds steam foruse in the evaporators. The exit gases from the waste heat boiler 65 ata temperature of 450 500 F. are carried through line 25 to the gascooler 68 where cooling water is introduced. The cooled gases containing626 pounds per hour of S0 and a large excess of CO are carried intoabsorber 80 and are brought into countercurrent contact with the sodiumaluminate solution to react therewith and form a mixture of 1,200 poundsper hour of sodium sulfite and 1,250 pounds per hour of sodium carbonatein solution and aluminum hydrate is precipitated as a slurry. The slurryis carried to the belt filter washer 14 where filter cake of aluminumhydrate is removed and dropped into the repulper 12. The filtratecontaining 1,200 pounds per hour of sodium sulfite, 1,250 pounds perhour of sodium carbonate and a small amount of sodium sulfide is carriedto pulp plant chemical storage 110.

EXAMPLE 2 83,000 pounds per hour of percent solids soda pulp blackliquor is concentrated in suitable multiple effect evaporators to 14,000pounds per hour of 60 percent solids black liquor containing 3,000pounds per hour of spent caustic soda. The concentrated liquor is fedthrough repulper l2 and mixer tank 16 where it is intimately mixed with10,000 pounds per hour of freshly precipitated aluminum hydrate filtercake containing 6,000 pounds of aluminum hydroxide Al (01-1 This mixtureis fed to the pelletizer 21 where it 47 by counter-current draft air.14,000 pounds per hour of kiln ash is recycled continuously through thegranulator 53 and ground ash bin 32 back into the pelletizer 21. 6,200pounds per hour of kiln ash is fed through dissolver mixer 92 wherewater is added to form a 20 percent solution of sodium aluminate. Thissolution is fed to absorber 80. Hot flue gases from the kiln 40 areexhausted through a cyclone 62 where ash fines are precipitated and canbe carried into the dissolver mixer 92 or put in the ground ash recyclescrew 31.

From the cyclone 62, the hot gases are carried to and through the wasteheat boiler 65 where heat is exchanged with water to generate 23,000pounds per hour of evaporator processed steam. The exit gases from theboiler 65 at a temperature of 450 500 F. are carried to the gas cooler68 and the cooled gases containing a large excess of CO are carried intothe absorber and are brought into contact countercurrently with thesodium aluminate solution entering the absorber from the mixer dissolver92. In the absorber, 4,000 pounds per hour of soda ash (NA- CO insolution are produced and aluminum hydrate is precipitated as a slurry.The slurry is carried through aging tank 101 into the belt washer 14where the aluminum hydrate filters cake is removed and carried into therepulper 12. The filtrate from the belt washer 14 is fed to storage orchemically processed in any desired manner, such as causticizing, forsubsequent use in the mill pulping operation.

EXAMPLE 3 Same as Example 1 except that, if only sodium sulfite isdesired as the final pulp chemical product, 380 pounds per hour ofelemental sulfur is fed to the rotary kiln 40 for combustion along withthe pellets to provide the needed amount of S0 to react with all of thesodium content of the liquor preferrential to reaction with CO EXAMPLE 4Same as Example 1, except that the spent sulfite liquor to be processedhas been modified to a raffinate resulting from the acidification ofconcentrated spent NSSC liquor with sulfuric acid stoichiometric to thesodium acetate and forrnate content followed by solvent extraction ofthe liberated acetic and formic acids with Thus, it may be seen thatthis invention has provided a practical and commercially usuable processand apparatus for treating concentrated spent liquor from a soda-basedpulping process to recover sodium for reuse in the pulping process andto prevent the usual pollution of streams and air caused by the usualeffluent from the pulping process.

In the drawings and specification, there have been set forth preferredembodiments of the invention, and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

That which is claimed is:

l. A process for treating concentrated spent liquor from a soda-basedpulping process to recover sodium for reuse in the pulping process andto prevent the usual pollution of streams and air caused by the usualeffluent from the pulping process; said treating process comprising: i

mixing concentrated spent liquor containing sodium from asoda-based'pulping process with recycled reactive alumina hydrate in anamount necessary to react with the sodium content of the liquor for theultimate formation of sodium aluminate as the reaction product;

spraying the concentrated liquor-alumina hydrate mixture onto a bed ofrecycled sodium aluminate furnace ash and tumbling the mixture and ashto form solid pellets thereof; combusting and reacting the solid pelletsby feeding the pellets through a furnace operating at a temperaturebelow the fusion temperature of sodium aluminate and at a sufficientlyhigh temperature to combust the organic portion of the pellets and reactthe sodium content thereof with the alumina to form additional sodiumaluminate ash; pulverizing the ash and recycling a portion thereof forsubsequent reuse in the formation of pellets; dissolving the remainingportion of the pulverized ash in water to form a solution of sodiumaluminate; reacting the sodium aluminate solution with sulphur dioxideto for-m sodium sulfite and alumina; and separating the alumina forreuse in the mixing step and the sodium sulfite for reuse in the pulpingprocess. H V

2. A process for treating concentrated spent liquor, as set forth inclaim 1, in which said combusting step is carried out at temperaturesbelow 3000 3. A process for treating concentrated spent liquor, as setforth in claim 2, in which said combusting step is carried out attemperatures between about 1500 F. to 2000 F.

4. A process for treating concentrated spent liquor, as set forth inclaim 1, in which the sodium aluminate a molarrat flilaz to A1103 9fabout '1 :1 923,

5. A process for treating concentrated spent liquor, as set forth inclaim 1, in which the concentrated spent liquor has a solids content offrom about 25% to 70% before mixing with alumina hydrate. V V

6. A process for treating concentrated spent liquor, as set forth inclaim 1, wherein the step of reacting the sodium aluminate solution withsulphur dioxide includes withdrawing gases containing sulphur dioxidefrom said combusting step and feeding the gases into contact with thesodium aluminate solution.

7. A process for treating concentrated liquor from a soda-base sulfitepulping process to recover sodium for reuse in the pulping process andto prevent the usual pollution of streams and air caused by the usualeffluent from the pulping process; said treating process comprising:

mixing concentrated spent liquor containing sodium and sulfur withrecycled reactive alumina hydrate in an amount necessary to react withthe sodium content of the liquor for the ultimate formation of sodiumaluminate as the reaction product;

spraying the concentrated liquor alumina hydrate mixture onto a bed ofrecycled sodium aluminate furnace ash and tumbling the mixture and ashto form solid pellets thereof;

combusting and reacting the solid pellets by feeding the pellets througha furnace operating at a temperature below the fusion temperature ofsodium aluminate and a sufficiently high temperature to combust theorganic portion of the pellets and react the sodium content thereofwiththe alumina to form additional sodium aluminate as a particulateunfused ash;

pulverizing the ash and recycling a portion thereof for subsequent reusein the formation of pellets; dissolving the remaining portion of thepulverized ash in water to form a solution of sodium aluminate;withdrawing flue gases containing sulphur dioxide and carbon dioxidefrom the combusting and reacting step and feeding the gases into contactwith the sodium aluminate solution;

reacting the sodium aluminate solution with the flue gases containingsulphur dioxide and carbon dioxide to form a mixture of sodium sulfiteandsodium carbonate in solution and aluminum hydrate as a slurry;

filtering and separating the aluminum hydrate for reuse in the mixingstep and separating the sodium sulfite and sodium carbonate for reuse inthe pulping process.

8. An apparatus for treating concentrated spent liquor from a soda-basedpulping process to recover sodium for reuse in the pulping process andto prevent the usual pollution of streams and air caused by the usualeffluent from the pulping process; said treating apparatus comprising:

means for mixing concentrated spent liquor containing sodium from asoda-based pulping operation with recycled reactive alumina hydrate inan amount necessary to react with the sodium content of the liquor forultimate formation of sodium aluminate as the reaction product;

means for forming solid pellets from the concentrated liquor-aluminumhydrate mixture comprising a rotating enclosed tumbling means carrying abed of recycled sodium aluminate furnace ash in the bottom thereof andspray means for spraying the concentrated liquor-aluminum hydratemixture 7 onto the bed of recycled sodium aluminate furnace ash so thatas the tumbling means rotates, solid pe1- lets will be formed;

furnace means for combusting and reacting the solid pellets andincluding means for feeding the pellets from the pellet forming means tothe furnace means, said furnace means operating at a temperature belowthe fusion temperature of sodium aluminate and at a sufficiently hightemperature to combust the organic portion of the pellets and react thesodium content thereof with alumina to form additional sodium aluminateas a particulate unfused ash;

pulverizing means for receiving the ash from said fur nace means and forpulverizing the same for subsequent use in the treating process;

means for recycling a portion of the pulverized ash to said pelletforming means for use in the formation of solid pellets therefrom;

means for receiving the remaining portion of the pulverized furnace ashand dissolving the same in water to form a solution of sodium aluminate;

means for receiving the sodium aluminate solution and reacting the samewith sulphur dioxide to form 15 sodium sulfite and alumina; and

means for separating the alumina for reuse in the mixing means and thesodium sulfite for reuse in the pulping process.

9. The apparatus for treating concentrated spent liquor, as set forth inclaim 8, in which said means for receiving the sodium aluminate solutionand reacting the same with sulphur dioxide comprises an elongatevertically extending hollow housing, a plurality of grids of spacedapart, parallel, generally cylindrical bars extending transverselyacross said housing wherein alternate grids of bars extend in oppositedirections at angles to each other so as to form venturi-like passagesbetween the bars and a generally checkerboard arrangement of grids ofbars so that the sodium aluminate solution may be introduced on top ofsaid grids of bars and flow by gravity flow down through saidventuri-like passages for intimate contact with the sulphur dioxide inthe form of gases which enter said housing from the bottom thereof andflow counter-currently to the solutron.

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,787,283 Dated January 22, 1974 Inventor) Donald R. Sheeley, et a1 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 3, line 3, change "siumina to --a1umina-; Column 3, line 38,after "sticky" insert --or-;

Column 8, Line 62, change "finate" to -butano'ne from the raffinatefollowed by additional raffinafe";

Column 12, line 1, change "The" to An--.

Signed and sealed this 6th day of August 197A.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM P0-1050 (10-69) I 1 USCOMM'DC 60376-P69 I 9 [L5 GOVERNMENTPRINTING OFFICE I959 O355-334

2. A process for treating concentrated spent liquor, as set forth inclaim 1, in which said combusting step is carried out at temperaturesbelow 3000* F.
 3. A process for treating concentrated spent liquor, asset forth in claim 2, in which said combusting step is carried out attemperatures between about 1500* F. to 2000* F.
 4. A process fortreating concentrated spent liquor, as set forth in claim 1, in whichthe sodium aluminate has a molar ratio of Na2O to A12O3 of about 1:1 to2:1.
 5. A process for treating concentrated spent liquor, as set forthin claim 1, in which the concentrated spent liquor has a solids contentof from about 25% to 70% before mixing with alumina hydrate.
 6. Aprocess for treating concentrated spent liquor, as set forth in claim 1,wherein the step of reacting the sodium aluminate solution with sulphurdioxide includes withdrawing gases containing sulphur dioxide from saidcombusting step and feeding the gases into contact with the sodiumaluminate solution.
 7. A process for treating concentrated liquor from asoda-base sulfite pulping process to recover sodium for reuse in thepulping process and to prevent the usual pollution of streams and aircaused by the usual effluent from the pulping process; said treatingprocess comprising: mixing concentrated spent liquor containing sodiumand sulfur with recycled reactive alumina hydrate in an amount necessaryto react with the sodium content of the liquor for the ultimateformation of sodium aluminate as the reaction product; spraying theconcentrated liquor-alumina hydrate mixture onto a bed of recycledsodium aluminate furnace ash and tumbling the mixture and ash to formsolid pellets thereof; combusting and reacting the solid pellets byfeeding the pellets through a furnace operating at a temperature belowthe fusion temperature of sodium aluminate and a sufficiently hightemperature to combust the organic portion of the pellets and react thesodium content thereof with the alumina to form additional sodiumaluminate as a particulate unfused ash; pulverizing the ash andrecycling a portion thereof for subsequent reuse in the formation ofpellets; dissolving the remaining portion of the pulverized ash in waterto form a solution of sodium aluminate; withdrawing flue gasescontaining sulphur dioxide and carbon dioxide from the combusting andreacting step and feeding the gases into contact with the sodiumaluminate solution; reacting the sodium aluminate solution with the fluegases containing sulphur dioxide and carbon dioxide to form a mixture ofsodium sulfite and sodium carbonate in solution and aluminum hydrate asa slurry; filtering and separating the aluminum hydrate for reuse in themixing step and separating the sodium sulfite and sodium carbonate forreuse in the pulping process.
 8. An apparatus for treating concentratedspent liquor from a soda-based pulping process to recover sodium forreuse in the pulping process and to prevent the usual pollution ofstreams and air caused by the usual effluent from the pulping process;said treating apparatus comprising: means for mixing concentrated spentliquor containing sodium from a soda-based pulping operation withrecycled reactive alumina hydrate in an amount necessary to react withthe sodium content of the liquor for ultimate formation of sodiumaluminate as the reaction product; means for forming solid pellets fromthe concentrated liquor-aluminum hydrate mixture comprising a rotatingenclosed tumbling means carrying a bed of recycled sodium aluminatefurnace ash in the bottom thereof and spray means for spraying theconcentrated liquor-aluMinum hydrate mixture onto the bed of recycledsodium aluminate furnace ash so that as the tumbling means rotates,solid pellets will be formed; furnace means for combusting and reactingthe solid pellets and including means for feeding the pellets from thepellet forming means to the furnace means, said furnace means operatingat a temperature below the fusion temperature of sodium aluminate and ata sufficiently high temperature to combust the organic portion of thepellets and react the sodium content thereof with alumina to formadditional sodium aluminate as a particulate unfused ash; pulverizingmeans for receiving the ash from said furnace means and for pulverizingthe same for subsequent use in the treating process; means for recyclinga portion of the pulverized ash to said pellet forming means for use inthe formation of solid pellets therefrom; means for receiving theremaining portion of the pulverized furnace ash and dissolving the samein water to form a solution of sodium aluminate; means for receiving thesodium aluminate solution and reacting the same with sulphur dioxide toform sodium sulfite and alumina; and means for separating the aluminafor reuse in the mixing means and the sodium sulfite for reuse in thepulping process.
 9. The apparatus for treating concentrated spentliquor, as set forth in claim 8, in which said means for receiving thesodium aluminate solution and reacting the same with sulphur dioxidecomprises an elongate vertically extending hollow housing, a pluralityof grids of spaced apart, parallel, generally cylindrical bars extendingtransversely across said housing wherein alternate grids of bars extendin opposite directions at 90* angles to each other so as to formventuri-like passages between the bars and a generally checkerboardarrangement of grids of bars so that the sodium aluminate solution maybe introduced on top of said grids of bars and flow by gravity flow downthrough said venturi-like passages for intimate contact with the sulphurdioxide in the form of gases which enter said housing from the bottomthereof and flow counter-currently to the solution.